Circuit assemblies, detection devices with such circuit assemblies as well as also lighting devices are comprehensively known in the prior art such that a separate printed evidence is not required hereto. Detection devices of the generic type are often used as motion sensors, which serve for controlling lighting devices among other things, namely with respect to their illumination function. A motion sensor is an electronic sensor unit, which is able to recognize motions of objects, in particular of living beings, preferably of persons, in its closer environment and to provide a corresponding sensor signal. For this purpose, the sensor unit can capture one or more different physical quantities. Additionally, it can for example also be provided that the sensor unit is formed to compare the respectively captured physical quantity to a comparative value and to output a corresponding sensor signal, which can already be a digital signal. However, the sensor unit is often formed to provide an analog sensor signal, which is associated with a current value of the respectively captured physical quantity. Usually, the sensor signal is an electrical signal. For further evaluating the sensor signal, therefore, a circuit assembly is usually connected to the sensor unit, which can for example be encompassed by a further evaluation unit or the like or also be connected to such an evaluation unit.
Usually, digital signal processing is provided by the evaluation unit, which can preferably also include signal transformations or the like among other things. For this reason, the circuit assembly usually includes the sample and hold circuit and a low-pass filter, which serves as an anti-aliasing filter, between its input terminal and its output terminal. The effect of aliasing is for example described in Nachrichtentechnik by Steinbruch, Rupprecht, volume II, Nachrichtenübertragung, 3rd edition, Springer Verlag, 1982, as well as also in Entwurf and Realisierung digitaler Filter by Seyed Ali Azizi, 3rd edition, Oldenbourg Verlag, 1987, as well as furthers.
In particular in lighting devices, the sensor unit is often constituted by a radar module. Due to legal requirements and/or requirements due to standardization, an energy consumption by the lighting device in a standby mode is limited. This means for the lighting device that if the lighting device is deactivated with respect to the light emission, the radar module is active to be able to ensure motion recognition for realizing the function of a motion sensor. Therein, a preset energy consumption must not be exceeded.
In order to achieve this, it is usual in the prior art to supply the radar module with electrical energy in clocked manner. However, additional measures are required hereto.
However, it proves obstructive therein that the analog electrical signal provided by the radar module has to be time-discretized by the evaluation unit for the later digital signal processing. The discretization is usually achieved by a sample and hold circuit, which results in a maximally possible upper limit of a signal frequency at the output of the radar module according to sampling rate. This maximum frequency of the analog electrical sensor signal of the radar module should be approximately half of the sampling rate. If this maximum frequency is exceeded by the analog electrical sensor signal, problems with respect to the digital signal processing can arise due to the sampling theorem as a result. For this reason, the above mentioned low-pass is usually provided, the cut-off frequency of which is usually chosen corresponding to half of the sampling rate, such that the above mentioned problems can be avoided.
However, the employment of the low-pass filter proves problematic if the detection device is supplied with electrical energy in clocked manner. The employment of the low-pass, as explained above, is opposed to the pulsed energy supply, in particular also because requirement with respect to a settling time and the cut-off frequency are not adaptable hereto.
Heretofore, it is provided that the clocked energy supply for the radar module is effected by switching on and off a supply voltage. Thereby, the operating duration of the radar module can be reduced to about 10%, whereupon the energy consumption can be correspondingly reduced by about 90%. The radar module generates a frequency-variable, sinusoidal analog electrical sensor signal, which is modulated on a direct current component. In order not to amplify the pulsed direct current component in a subsequent amplifier circuit and thereby cause overload, this signal is stored until the next pulse by a sample and hold circuit.
Even if the above mentioned approach has proved itself, thus, the possibilities of employment are limited and the effort is high.
Therefore, the invention is based on the object to provide an improved circuit assembly as well as an improved detection device and an improved lighting device.